A variety of track type tractors, front-end loaders and other relatively large machines include a cab mounted on a machine body. An operator sits inside the cab, from which he or she can drive and operate the machine. Access to the cab is typically by way of steps or a ladder on the side of the body, allowing an operator or service technician to climb to an operator platform adjacent to or surrounding the cab.
Such machines often operate in rugged terrain such as above-ground and underground mines, construction and demolition sites and similarly extreme environments, subjecting the machine and machine body to constant wear and tear. For example, a track type tractor pushing a large pile of rubble may be travelling essentially through a sea of rock to clear a path across a work surface. Thus, virtually all machine components are robust and durable to withstand the frequent scrapes, impacts and other forces encountered during operation.
Access systems such as ladders and steps can be located on the exterior of the machine. Accordingly, as a machine operates, the external ladders, steps, etc. can be damaged by rock, trees and other materials through which the machine passes. A ladder extending to the side of a machine can be shorn off by passing work material. Similarly, steps on the side of the machine can be dented, scraped, smoothed or otherwise rendered unsuitable for easy access or egress to the machine cab by an operator. Further, the ladder can be damaged or torn off if the operator lifts the blade of the machine without stowing the ladder.
The above concerns have prompted designers to propose various means for accessing the cab via a retractable or otherwise displaceable ladder system. When the operator needs to climb to or from the cab, a ladder can be deployed as needed. When the machine is operating, the ladder can supposedly be stowed out of the way. One access ladder design is known from U.S. Pat. No. 5,988,316 to Hedley. Hedley '316 includes a powered ladder system pivotably connected to a rotary axle. Hedley '316 proposes moving the ladder between a use position and a storage position by initially rotating the ladder in a first direction, pivoting the same upwardly, then rotating the ladder in a second direction and eventually stowing the same. Hedley '316 thus uses a relatively complex process, requiring a plurality of steps and rotational axes to stow or deploy the ladder.